Today, off-highway trucks are used to mine many minerals for further refining and clay type overburden or cover materials. The mining of various types of materials is relatively straightforward, although the complexity of the mining is increased by 1) the natural cohesive characteristics of many materials, 2) the amount of material being mined/hauled and 3) the environmental conditions under which it is mined.
In their natural state, many mined materials are extremely sticky and these mined materials naturally freely cling to each other. This can result in a buildup of material on the truck body surfaces, etc. that contact such materials. For example, walking around on some materials (such as clay type materials) will quickly result in the soles of a person's shoes building up with layers of material that can easily buildup to 8 to 10 mm thick.
This same sort of buildup happens in truck bodies. A common condition that occurs during the use of truck bodies is the buildup of “carryback.” As successive loads are hauled, sticky hauled material begins to incrementally buildup in the interior of the body with each load until the body retains a significant amount of material between successive loads. Experience has shown that initial load carryback begins in those areas of a truck body where intersecting walls of a truck body meet.
This build up of material or “carryback” is significant for very sticky materials. The characteristics of materials which stick together and coagulate are exacerbated as material in its natural state is disturbed by the mining process. With these sorts of materials, the buildup of carryback happens quickly and is significant. This significant carryback reduces the effective capacity of the truck body and reduces the efficiency of the truck and the overall mining operation.
Mine loading shovels weigh in at 1450 to 1800 tons and off-highway trucks weigh in at 550 to 600 tons. As loading shovel buckets dig into the materials being mined and load or “drop” 100 tons at a time of material into off-highway truck bodies, the materials are further compressed in the off-highway truck body. Also, as material is hauled in an off-highway truck body the material is further compacted as off-highway trucks navigate the mine haul roads to their destination, vibrating the load, causing settling of the load in the off-highway truck body. By the time an off-highway truck reaches its destination, in some cases the shaking and resulting settling of the hauled load results in the hauled materials amalgamating into almost a solid packed mass.
The circumstances of mining and hauling in combination with the cohesive coagulating characteristics of some hauled materials results in the hauled materials in some cases dumping from the truck body as a solid mass or “loaf.” As loads of material “loafs” exit truck bodies, the truck chassis itself is subjected to extreme ‘jolts,’ resulting in severe truck driver discomfort. Drivers of trucks hauling materials which “loaf” are often exposed to extreme ‘whole body vibration’ as loads of “loafs” are dumped.